A furnace uses fan-generated forced air to supply heat through duct work to vents throughout a home or other building. The heated air circulates and then is returned to the furnace through return duct work or a central return through a filter in front of the furnace.

Function

A furnace filter cleans the air that is returned to the furnace. Air that has moved through a building collects and carries dust and other air-born debris. The air must be cleaned before being redistributed so that it does not circulate contaminants.

Description

A furnace filter screen is made of paper fiber or metal. The screen mesh is fine and constructed of multiple layers, in a pleated pattern, designed to catch dust and tiny particulates. Most furnace filters are electrostatic. A furnace filter is framed with cardboard.

Types

Furnace filters are available in various dimensions to fit specific types of furnaces. The filter fits in a filter frame on the air-intake side of the furnace. The length, width and thickness for the filter is specified by the furnace manufacturer.

Problems

If a furnace filter screen becomes dirty and clogged, the filter limits air flow and causes inefficient furnace function. A dirty furnace filter can inhibit the heating and cause higher utility costs.

Expert Insight

Furnace filters should be replaced once a month, or more often if indoor air quality affects allergies and respiratory problems.

Source:

Furnace Filter Care:

American Lung Association: Furnace Filters

CMHC: Your Furnace Filter